At the present time electroencephalography (EEG), the detection and amplification of electrical brain waves, often uses a small number of electrodes, for example 4-12, which are removably secured to the scalp of the person being tested. A larger number of electrodes is used in the EEG "International 10/20 System".
It has been suggested that greater detail regarding brain wave activity may be obtained if a larger number of electrodes are used. The brain waves of a subject, after being amplified, digitized and analyzed in a computer system, may be displayed in a topological map. In such a map, brain wave activity in various areas is shown, for example, using a color scale. Such maps are more realistic and reliable if they are obtained from closely spaced sensors, i.e., from many EEG electrodes. Consequently, it has been argued that the preferred number of EEG electrodes is at least 64, and most preferably 128 or more.
At the present time, under some conditions, satisfactory and consistent results are obtainable with EEG electrodes by using an electrolyte (electrically conductive fluid), such as a solution or gel. The use of dry electrodes (without electrolyte) is often more convenient; however, dry electrodes often present problems in obtaining a constant low impedance contact with the scalp.
The use of an electrolyte also may present problems, as the fluid may have a tendency to spread over the scalp, possibly electrically shorting electrodes, and may be messy and difficult to remove. One type of EEG "wet" (electrolyte) electrode uses a small inverted cup-like structure which is filled with electrolyte by a technician before the electrodes are applied to the scalp. However, when the electrode set consists of a large number of electrodes (over 64), in a helmet, hat or web, the filling of the electrodes with electrolyte is time-consuming. Since that task takes so long, for example an hour, some of the electrodes may be missed and left without electrolyte.
The use of a large number (over 32) of EEG electrodes is discussed in U.S. Pat. No. 4,736,751 entitled "Brain Wave Source Network Location Scanning Method And System", which mentions the use of as many as 256 electrodes.
The use of conductive fluid or gel on EEG electrodes is shown in prior patents. In U.S. Pat. No. 4,595,013 entitled "Electrode Harness" conductive gel is applied to foam 58 within reservoirs 56. In U.S. Pat. No. 4,709,702 entitled "Electroencephalographic Cap", electrolyte is pumped from pump 60 through tube 50 to the area of penetration of the probe 31 (electrode). U.S. Pat. No. 4,537,198 entitled "Electrode Cap" uses an electrode having a washer-like foam pad 60 and a central opening through which passes a "semi-liquid or paste-like" electrolyte. In U.S. Pat. No. 4,683,892 entitled "Method And Apparatus For Conducting Brain Function Diagnostic Test", an electrolyte solution is fed through conduit 53 and the open lower end of a contact 50A to permit introduction of the electrolyte directly on the scalp of the person being tested.